This invention relates to a water-deionizing system for producing ultrapure water having a specific electric conductivity of the order of less than 0.1 .mu.S(micro Siemens)/cm at 25.degree. C.
The demand for ultrapure water is ever increasing for washing various electronic and other devices to remove electrolytic contaminants of which presence adversely affects the performance of such devices.
Ultrapure water may be conventionally produced by polishing suitable raw water such as from public water supply using various water-purifying techniques such as reverse osmosis, electrodialysis, deionization, distillation and the like. Usually a plurality of these techniques is employed in combination. In order to produce ultrapure water having a specific electric conductivity close to the theoretical limit of 0.05 .mu.S/cm at 25.degree. C., it is essential to treat water with both cationic and anionic ion-exchangers. This deionizing step may be conveniently accomplished by using commercially available cartridges commonly referred to as "water polisher" containing both anionic and cationic ion-exchangers as a mixed bed. Unfortunately, such cartridges are of limited use for producing a large quantity of ultrapure water for washing and other purposes because they are not practically capable of regenerating their ion-exchange capacities and thus have to be disposed once their capacities have been essentially saturated. Since these cartridges are usually prefilled with an intimate mixture of anion and cation exchangers and since separate regenerating agents are required for anion and cation exchangers, the mixture must be separated into its components before permitting the regeneration thereof. However, experiments have shown that this separation is practically very difficult to perform at water-purifying plants.
Accordingly, it is a principal object of the present invention to provide a water-deionizing system for producing ultrapure water which is simple in construction, easy in operation and suitable for treating water at sites where a relatively large amount of water is needed for washing and other purposes.
It is another principal object of the present invention to provide such a water-deionizing system which permits regeneration and repeated use of ion-exchangers.
Other objects and advantages will be apparent to those skilled in the art as the description proceeds.